How do you cancel with these people?

I called Telkom on 30/11/2017 to cancel my line rental effective 31/12/2017. I did this to ensure a full months notice. The call center agent advised to e-mail ********** as they don't cancel without the e-mail that has their cancellation application, copy of my ID and for good measure I even included my last invoice. I tried to call repeatedly to confirm they had this but my limit of being on hold in 20 minutes, then you clearly don't care for my business or time. In January i received another invoice, to which I tried to call the numbers on the invoice, no avail, tried to e-mail the only other e-mail address on the invoice ********** which is not a valid e-mail address and I sent a query for why I was still receiving invoices to ********** and have yet to received a response. I received another even larger invoice on 09/02/2018 and called 10210, who answered after 7 minutes only to tell me I need to call the sales department on 10213. I called this number and after 26min28sec and needing to get to a meeting I finally gave up. I gave the necessary notice, and I gave the necessary documents, so why won't Telkom cancel my line??

I have absolutely no intention in paying additional past December due to the incompetence shown by Telkom and I can assure you that I will never make the mistake of renting a line again from Telkom. I would rather be ********** completely by a company that will be available for me to upgrade, buy or leave.